Conventionally, as a memory system, an SSD (Solid State Drive) provided with a NAND flash memory (hereinafter, referred to as a “NAND memory”) is known. In the NAND memory, a unit of reading and writing is smaller than a unit of erasing. Before the writing, the erasing needs to be operated. According to this characteristic of the NAND memory, the SSD associates a logical address designated as a location where a host performs a read operation with a physical address indicating a physical location of the NAND memory. The SSD stores therein a relation between the logical address and the physical address as translation information. The SSD loads the translation information from the NAND memory to a RAM, and performs updating or referring to the translation information on the RAM.